“Nobody knows what started the argument but I was told it was something small that spiralled out of control.”

Abbie McCleary, from Ayr, witnessed Susan’s meltdown and posted on Twitter: “Can’t believe Susan Boyle was in the queue behind us at London to go into our flight and she took a tantrum and wasn’t allowed on the plane.

(Image: WireImage)

Mark Reynolds also wrote: “A quite surreal welcome back to the UK, with Susan Boyle throwing a massive child-tantrum right by me at Heathrow Terminal 5.”

Susan, who became an international star after stunning the world with her voice on Britain’s Got Talent in 2009, was at the airport waiting to catch a flight back to Glasgow.